KR101492282B1 - Method and apparatus for enhanced fiber bundle dispersion with a divergent fiber draw unit - Google Patents

Abstract

According to the present invention there is provided a method and associated apparatus for melt extruding a nonwoven web comprising providing a plurality of fibers from an extrusion apparatus. The fibers are transported through the branched profile portion of a fiber drawing unit (FDU) which causes the fibers to disperse and unfold in the machine direction in the FDU. The fibers are then transported through a branched diffusion chamber spaced from the outlet of the FDU to reduce the speed of the fibers and further unfold the fibers in the machine direction. The fibers can be charged in the diffusion chamber or in the FDU. From the outlet of the diffusion chamber, the fibers are placed on the forming surface as a nonwoven web.

A diffusion chamber, an extrusion apparatus, a fiber stretching unit, an elongation slot, a branching profile unit,

Description

[0001] METHOD AND APPARATUS FOR ENHANCED FIBER BUNDLE DISPERSION WITH A DIVERGENT FIBER DRAW UNIT [0002]

The present invention relates to a method for forming a nonwoven web and an apparatus for forming such a web.

Melt extruded nonwoven webs have many uses, including medical sanitary garments and articles, protective wear garments, funeral and veterinary products, and personal hygiene products. For this purpose, nonwoven fibrous webs provide tactile, comfort and aesthetic properties comparable to conventional woven or knitted fabrics. In addition, since the nonwoven web material can be formed into a filter mesh of fine fibers having a low pressure drop across the mesh while having a low average pore size suitable for capturing particulate matter, filtration for both liquids and gases It is widely used as a medium or an air filtering application.

Melt extrusion processes for spinning fibers such as continuous filament yarns, filaments or spunbond fibers and for spinning fine fibers such as meltblown fibers are well known in the art as well as related methods for forming nonwoven webs or fabrics therefrom . Typically, a fibrous nonwoven web such as a spunbond nonwoven web is formed by a fiber extrusion device, such as a spinneret, and a fiber attenuation device oriented in a cross machine direction ("CD "), such as a fiber stretching unit (FDU). That is, the device is oriented at a 90 degree angle to the web manufacturing direction ("machine direction" or "MD"). Although the fibers are generally placed on the forming surface in a random fashion, the resulting nonwoven web has overall average fiber orientation, because the fibers are emitted at the CD orientation spinnerets and the FDU and deposited on the MD transfer forming surface, The fibers are oriented to the MD rather than the CD. The fiber diffuser may be disposed below the FDU to reduce the fiber speed before placing the fiber on the forming surface. It is widely recognized that properties such as material tensile strength, porosity, permeability, extensibility and material barrier properties are, for example, a function of the uniformity and directionality of the material of the fibers or filaments of the web.

Using static electricity to impart charge to the fibers or filaments, using a dispersing device to direct the fibers and filaments to the desired orientation, using mechanical deflecting means for the same purpose, Have been made to distribute fibers or filaments within the web in a controlled manner. For example, WO 2005/045116 describes a method and apparatus for the production of a nonwoven web material in which the fibers are attenuated with a fiber stretcher and the speed of the fibers is reduced in a downstream diffusion chamber formed between opposing separation sidewalls . The electrostatically charged fibers are applied to the fibers before entering the diffusion chamber or into the diffusion chamber by two or more opposing electrostatic charging units.

WO 02/052071 describes a method and apparatus for the production of a nonwoven web material in which an electrostatic charge is applied to the fibers, which is then subjected to charge and is directed to the deflector device. The fibers are then collected on a forming surface to form a nonwoven web. The deflector device may comprise a series of teeth separated by a distance determined by the desired orientation of the fibers of the nonwoven web.

The prior art continues to seek improved methods and devices to further improve the process of distributing fibers in a melt extrusion process to achieve better nonwoven materials. The present invention relates to such an improved method and apparatus.

SUMMARY OF THE INVENTION [

BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of the present invention will become more apparent from the following detailed description or the accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification.

The present invention provides a method and associated apparatus for making a nonwoven web, the method comprising the steps of providing a plurality of fibers from an open melt extrusion system. After leaving the extruder device, such as a conventional spinneret, the fibers are quenched and then subjected to an air pressure damping force by an elongated slot of a detachable fiber elongation unit (FDU) having an inlet and an outlet, And the fibers are attenuated (reduced in diameter) in the quenching zone. In an open system, quenching air is provided by one or more blowers, and the air pressure damping force is controlled by any combination of air nozzles or plenums (collectively referred to as air nozzles) that induce relatively high velocity intake air through the elongate slots May be generated within the detachable FDU. In a closed system, the FDU is typically associated with a quenching air housing such that quenching air also acts as damping air. In certain configurations of the FDU, some degree of fiber attenuation may also occur in the FDU.

It may be desirable to perturb the attenuator flow within the elongated slot of the FDU to further improve the machine direction bundle dispersion of the fiber bundle. This can be done, for example, by alternately vibrating air from the air nozzles of the opposing walls of the FDU. This feature can be achieved with single or multiple air nozzles of each FDU wall.

From the FDU, the fibers are transported through a branched diffusion chamber spaced from the outlet of the FDU, and the speed of the fibers is reduced. Further, the fibers may be subjected to a static charge applied in a diffusion chamber or an FDU. The fibers exit the diffusion chamber and are collected as a web on a transfer forming surface.

It is known that slot elongation and fiber elongation units and linear elongation devices using high speed jets to impart stretching power to the fibers compress or densify the fiber bundles in the fiber / air stream. This densified or compressed fiber bundle then needs to be expanded to form the desired web. Diffusers and other types of fiber deflectors or dispersers and static electricity are used to inflate the fibers to ensure a high level of dispersion prior to the web forming process.

A unique feature of the method and apparatus of the present invention comprises transporting the fibers through the branched profiled portion of the FDU elongated slot to expand and spread the fibers in the machine direction in the FDU. The bifurcated profile causes the fiber bundle to expand and unfold in the machine direction in the draw slot before the entrance of the diffuser. This machine direction expansion of the fiber bundle within the FDU coupled with the bifurcated diffuser results in improved web formation as compared to a linear extension slot (parallel sidewall) or a converging extension slot (converging sidewall) under similar process parameters.

The bifurcated profile portion of the FDU elongated slot can take a variety of shapes. In one embodiment, the branching portion is formed by symmetrically branching sidewalls (curved, straight, or a combination thereof) of the FDU such that a symmetric branching angle is formed with respect to the longitudinal centerline of the elongated slot. In an alternative embodiment, the branched portion is formed by asymmetric branched sidewalls or one branched sidewall. The bifurcated portion of the elongated slot may be substantially continuous (at a constant or varying rate) from the minimum width to the maximum width. Alternatively, the branching portion can be branched in a discontinuous manner (e.g., stepped) between the minimum width and the maximum width.

The bifurcated profile portion of the FDU may include an elongated slot of total longitudinal length. For example, the elongated slot can be branched from the minimum width at the entrance of the elongated slot to the maximum width at the exit of the elongated slot. In another embodiment, the bifurcated profile portion may be formed only on a portion of the entire length of the elongated slot. For example, the FDU elongation slot may include an upstream (in relation to the fiber transport direction) unbranched portion adjacent to the bifurcated profile portion. This non-split portion may have basically parallel sidewalls or converging sidewalls.

The bifurcated profile portion of the FDU may be formed by a combination of a curved wall section, a straight wall section, or a curved and straight wall section.

Similar to the bifurcated profile portion of the FDU elongated slot, the bifurcated diffusion chamber may be formed by symmetrical or asymmetric bifurcated sidewalls.

In certain embodiments, as the fibers are transported through the FDU elongation slot by one or more electrostatic charging units, a static charge is applied to the fibers. For example, charge may be applied to an oppositely electrostatic charging unit in the FDU, where one of the electrostatic charging units is positioned substantially closer to the diffusion chamber than the other electrostatic charging unit. In alternate embodiments, a static charge is applied to the fibers as the fibers are transported through the diffusion chamber by, for example, opposing electrostatic charging units in the diffusion chamber.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of an exemplary prior art process for making a nonwoven web.

Figures 2A-2G are schematic diagrams of various embodiments of a fiber elongation unit in accordance with an aspect of the present invention.

3 is a schematic diagram of an exemplary prior art diffusion chamber configuration.

Justice

The term "polymer" as used herein generally includes, but is not limited to, homopolymers and copolymers such as blocks, grafts, random and alternating copolymers, terpolymers and the like, and blends and modifications thereof. Also, unless otherwise specifically limited, the term "polymer" should include all possible geometric configurations of the chemical structure. These configurations include, but are not limited to, isotatic, syndiotactic, and random symmetry.

The term "fiber" as used herein refers to both staple length fibers and continuous fibers, unless otherwise indicated. The term "fiber bundle" refers to a group of individual fibers.

The term "nonwoven web" or "nonwoven material" as used herein refers to a web having the structure of individual fibers or filaments that are interleaved but are not interleaved in a discernible manner, such as a knit or woven fabric. The nonwoven web can be formed by many processes, such as, for example, a meltblowing process, a spunbonding process, an air-lean process, and a carded web process. The basis weight of the nonwoven is mainly expressed in grams per square meter (gsm) or ounces of material per square yard (osy), and the fiber diameter is often expressed in micrometers.

The term " spunbond "or" spunbond nonwoven web "refers to a nonwoven fiber or filament material of small diameter fibers formed by extruding molten thermoplastic polymer from a plurality of capillaries of an spinnerette into fibers. The extruded fibers are cooled by being inferred or stretched by a known stretching mechanism. The stretched fibers are deposited or laid on the forming surface in a generally random manner to form a loosely entangled fiber web, and a bonding process is then applied to impart the fiber thereon with physical gatherability and dimensional stability. The manufacture of spunbond fabrics is described, for example, in U.S. Patent No. 4,340,563 to Appel et al., U.S. Patent No. 3,692,618 to Dorschner et al, and U.S. Patent No. 3,692,618 to Matsuki et al. 3,802,817. Typically, spunbond fibers or filaments have a weight per unit length of greater than about 1 denier and less than about 6 deniers, but finer yet heavier spunbond fibers can be produced. For fiber diameters, the spunbond fibers have predominantly an average diameter of greater than 7 micrometers, more specifically from about 10 micrometers to about 25 micrometers, and up to about 30 micrometers.

Reference will now be made to specific embodiments of the novel method and apparatus in accordance with the invention, one or more examples of which are illustrated in the drawings. It is to be understood that the embodiments are provided to illustrate the invention and are not intended to limit the invention. For example, features illustrated or described with respect to one embodiment may be used in other embodiments to yield yet another embodiment. The present invention includes these and other variations made with respect to the embodiments described and illustrated herein.

Figure 1 corresponds to Figure 1 of the prior art PCT Publication No. WO 2005/045116 and is used herein to describe various conventional features of the method and apparatus of the present invention for forming a nonwoven web in a melt extrusion process. Referring to Figure 1, a process line 10 is provided for the production of single component or multiple component continuous fibers. The process line 10 is an open system and includes an extrusion device such as a conventional extruder 30 for melting and extruding the polymer supplied from the polymer hopper 20. The polymer is fed from the extruder 30 through the polymer conduit 40 to the spinnerette 50 which forms the fibers 60 which can be single component or multicomponent fibers. When multi-component fibers are required, a second extruder fed from a second polymer hopper will be used. The spinnerette (50) has one or more rows of aligned openings or capillaries. The spinnerette opening forms a downwardly extending "curtain" or "bundle" of the fibers 60 as the polymer is extruded through the spinnerette 50. The spinnerette 50 for extruding the multi-component continuous fibers is known in the art and need not be described in detail herein. An exemplary spin pack for making multi-component fibers is described in U.S. Patent No. 5,989,004 to Cook, the entire contents of which are incorporated herein by reference for all purposes.

Polymers suitable for the present invention include materials known to those skilled in the art of making nonwoven webs and materials such as, for example, polyolefins, polyesters, polyamides, polycarbonates and copolymers, and blends thereof. It is to be understood that certain types of polymers are not limiting features.

1 also includes a quenching blower 64 disposed adjacent a curtain of fibers 60 extending from the spinnerette 50. The quenching blower 64, Air from the quenching air blower 64 quenched the fibers 60 extending from the spinnerette 50. As shown in Fig. 1, the quenching air can be directed from one side of the fiber curtain or from both sides of the fiber curtain. As used herein, the term "quenching " refers to means for reducing the temperature of a fiber using only a cooler medium than the fiber, such as, for example, a cooled air stream, an atmospheric temperature stream, or a moderate to moderately heated air stream .

An inhaler or "fiber elongating unit" (FDU) 70 is positioned below the spinnerette 50 to receive a curtain or bundle of quenched fibers, spaced from the spinnerette 50. The function and operation of a fiber drawing unit for use in a melt-spinning polymer is well known in the art. Generally, the fiber elongating unit 70 includes an elongated vertical passageway or elongated slot formed by the parallel side walls of the FDU 70, through which the fibers generally enter from both sides of the elongated slot and pass downwardly And is drawn by the flowing intake air. The attenuation chamber or fiber elongation slot is formed by the opposing plates or sidewalls designated 72 and 74 in FIG. In various prior art configurations, including the configuration of Figure 1, the opposing side walls 72, 74 are substantially parallel to one another and generally perpendicular to the horizontal plane. The fiber stretching unit 70 stretches the fiber through the slot using a moving air pressure stream such as intake air supplied by a blower (not shown). The intake air may or may not be heated. The intake air accelerates the fibers and applies damping or stretching forces on the fibers to reduce the diameter of the fibers. In addition, the intake air serves to guide and pull the curtain or bundle of fibers through the elongated slots of the fiber drawing unit 70. The intake air may be heated to activate potential spiral wrinkles in the multi-component fibers, for example, before the fibers are laid.

After the fibers are discharged from the fiber drawing unit 70, they pass through the diffusion chamber 80 to reduce the fiber speed before the fibers are placed on the nonwoven web. A typical diffusion chamber or diffuser is disclosed in U.S. Patent No. 5,814,349 to Geus et al., Which is hereby incorporated by reference in its entirety for all purposes. Other diffusion chamber configurations are also disclosed in U.S. Patent Nos. 6,918,750 and 6,932,590 to Zeus et al. As disclosed in U.S. Patent No. 5,814,349, the diffuser is preferably mounted slightly below the outlet of the fiber elongation unit so that the atmosphere is sucked into the diffusion chamber from the side.

Preferably, as shown in FIG. 1, a diffusion chamber 80 is formed between the opposing branch sidewalls 82, 84. The opposed sidewalls 82,84 branch outwardly toward the outlet of the chamber 80 in such a way that the volume of the chamber formed between the sidewalls expands toward the lower end of the diffuser. Preferably, the opposing sidewalls 82, 84 are substantially continuous and non-vented so that air from the jet of attenuating air does not escape from the walls of the diffusion chamber, but rather exits the lower portion after passing through the diffusion chamber 80 . The gradual expansion or increase of the volume of the diffusion chamber 80 causes the jets of rapidly moving attenuating air to expand from the fiber draw unit 70 and progressively expand to an increasing volume as it passes through the diffusion chamber 80. The branched side walls 82,84 may be substantially parallel to each other at the top of the diffusion chamber 80 and be inclined or branched at an angle of about 5 degrees from the vertical centerline of the chamber at the point where they start to branch from each other. Thus, the sidewalls of the diffusion chamber 80 and thus the divergence angle can be adjustable, and the divergence angle can be much smaller than 5 degrees or much larger than 5 degrees.

As the pneumatic jet expands in the diffusion chamber 80, the pneumatic jet decreases in speed and also decreases in fiber speed, causing the fiber bundle to unfold somewhat in the machine direction. That is, as the fiber bundle moves down through the diffusion chamber, it begins to take a somewhat larger machine direction dimension than it had at the exit of the fiber drawing unit 70.

However, in order to provide high uniformity material formation on the placed fibers, it is highly desirable that the machine direction fiber bundle spread out is larger than the bundle spread created by the diffusion chamber alone. In this regard, as the fibers move through the elongated slots of the fiber drawing unit 70, or as the fibers move through the diffusion chamber 80, or through both, One or more electrostatic charging devices may be used to impart a static charge. In Fig. 1, exemplary electrostatic charging units 76, 78 are shown in opposed relationship located on opposing side walls 72, 74 of fiber elongating unit 70. When an opposite electrostatic charging unit is used, the opposing electrostatic charging unit can be configured to be offset or staggered so that the one electrostatic charging unit is higher or lower than the other. For example, referring to FIG. 1, electrostatic charging unit 78 is mounted on each sidewall lower, i.e. closer to the diffusion chamber than electrostatic charging unit 76. Generally speaking, electrostatic charging devices, such as charging units 76 and 78, can consist of one or more rows of electro-emitter fins that generate a corona discharge to impart an electrostatic charge to the fibers, which, once charged, And will tend to prevent groups of individual fibers from agglomerating or "roping" one another. Exemplary processes for charging fibers to produce a nonwoven having improved fiber distribution are disclosed in U.S. Patent No. 5,204,508, to Haynes, et al., Published on July 4,2002, the disclosure of which is incorporated herein by reference for all purposes, Is disclosed in published patent application WO 02/52071. The function and operation of such electrostatic charging devices are well known in the art and need not be described in detail herein.

In another embodiment for assisting machine direction bundle spreading, it may be desirable to utilize one or more electrostatic charging units within the diffusion chamber 80. For example, one or more electrostatic charging units may be located on the same diffusion chamber sidewall. It may also be desirable to have at least one electrostatic charging unit located on each side wall of the diffusion chamber. When the electrostatic charging unit is located on both side walls, the electrostatic charging unit can be positioned substantially directly opposite to each other, i.e., the electrostatic charging unit can be positioned at substantially the same vertical height in the diffusion chamber 80. [ Similar to the staggered arrangement described with respect to the electrostatic charging units 76, 78 of the fiber drawing unit 70 of Fig. 1, it is advantageous to have an electrostatic charging unit in the diffusion chamber located in a staggered arrangement .

In another embodiment, a single electrostatic charging unit can be used in the diffusion chamber or in the fiber stretch slot with a specific application of aerodynamic power to balance the repulsive force generated by the electrostatic charging unit. For example, although it has been described above with reference to Fig. 1 that the fibers are drawn through the drawn slots of the fiber drawing unit, generally by suction air entering from both sides of the aisle, the electrostatic charging unit forms the drawn slots of the fiber drawing unit When positioned on only one of the walls, the fiber bundle spreading in the machine direction can be improved by using attenuated air entering the fiber drawing unit from only the opposite side walls of the fiber drawing unit.

2A-2G illustrate aspects of various fiber elongating units 270 in accordance with the method and apparatus of the present invention that may be used in the process line or other suitable process line shown in FIG. It is to be understood that the above description is schematic and overall exaggerated in order to more clearly illustrate the aspects of the present invention.

Referring to FIG. 2A, the process line 200 is shown as an extrusion device in the form of a spinnerette 250 for forming individual fibers from a molten polymer, as described above. The double quenching air blower 264 is provided at the outlet of the spinnerette 250. A fiber drawing unit (FDU) 270 having an inlet 271 and an outlet 275 receives the quenched fiber. The attenuated air (heated or unheated) is directed to the FDU 270 by any combination of nozzles, plenums or jets 210 (collectively referred to as nozzles). In the illustrated embodiment, two nozzles 210 are provided in each wall 272, 274. As will be described in more detail below, these dual air nozzles are located very close to or at the bifurcation of the sidewalls 272, 274. It should be understood that any number, configuration, and position of the nozzles 210 for supplying the attenuating air within the FDU are within the scope and spirit of the present invention.

To further enhance the machine direction spreading of the fiber bundles, it may be desirable to perturb the air supplied by the nozzles 210 by, for example, vibrating or otherwise disturbing or otherwise confining the airflow. This can be accomplished by using one or more mechanical valves that alternately vibrate or deform the air flow supplied to the nozzle 210. This perturbation can be achieved with single, dual or other multiple arrangements of nozzles 210 within each wall 272, 274 of the FDU. The perturbation of the drawn air is described in U.S. Patent No. 5,807,795 to Lau et al., Which is hereby incorporated by reference in its entirety for all purposes.

A branching diffusion chamber 280 having an inlet 286 and an outlet 288 and having symmetrical branch walls 282 and 284 is disposed below the outlet 275 and acts as described above. Generally, the outlet 275 of the FDU 270 has a width that is less than or equal to the width of the inlet 286 to the diffusion chamber 280. The fibers are discharged from the diffusion chamber 280 and laid on a conveying belt 212 (110 in FIG. 1), such as a nonwoven web.

Referring again to Figure 2A, the FDU 270 forms an elongated slot 273 that includes a bifurcated profile portion 277. [ Generally, the bifurcated profile portion is the longitudinal portion of the elongated slot 273, and the cross-sectional width of the slot 273 increases from a minimum value to a maximum value. 2A, the bifurcated profile portion 277 generally corresponds to the overall length of the elongated slot 273, the entrance 271 of the elongated slot forms a minimum width, and the outlet 275 has a maximum Width. The profiled profile portion 277 of this embodiment has a generally constant bend angle formed by the symmetrically branched side walls 272, 274. With respect to the longitudinal centerline of the elongated slot 273, the walls 272 and 274 are equally branched over the length of the slot 273. As described above, the branched profile portion 277 of the FDU allows fibers transported through the elongated slot to open or expand in the machine direction before exiting the FDU outlet 275 and before entering the diffusion chamber 280. It is believed that this initial machine direction spreading does not adversely affect the degree of attenuation in the FDU 270 and thus significantly improves the function of the diffuser with little effect on fiber size. The branched profile portion 277 does not require increased energy (i.e., increased damping air pressure) to provide an improved nonwoven web and to provide this benefit.

Although the wall of the FDU 270 of Figures 2A-2G is shown as being straight (not curved), the wall may be curved to achieve the purpose of the branched profile portion 277 of the elongated slot 273, It should be appreciated that a combination of a straight and a straight wall may be included.

Figure 2B shows an embodiment of the FDU 270 in which the branched profile portion 277 is less than the entire length of the elongated slot 273. [ In this embodiment, the side walls 272, 274 are essentially parallel from the inlet 271 to a downstream position within the FDU where the walls 272, 274 are symmetrically branched to the outlet 275. Thus, in front of the bifurcated profile portion 277 there is an initially unstructured portion of the elongated slot 273 defined by the parallel sidewalls.

As in Fig. 2A, the bifurcated profile portion 277 of Fig. 2B is formed by a generally continuous wall portion (straight or curved). It should be appreciated that the bifurcated profile portion 277 may be formed by a discontinuous wall profile, such as a stepped profile. Various branching profiles can be used to achieve the purpose and function of the branching profile portion 277 within the scope and spirit of the present invention.

2B also includes one or more electrostatic charging units 276, 278 within the bifurcated diffusion chamber 280 as described above. These units may be directly opposed as shown in the figures or may be provided in a staggered arrangement. In addition, any one embodiment of Figures 2A through 2G may include any combination of charging units within the FDU 20, such as the units 276 and 278 of Figure 2C.

Figure 2C shows an embodiment of FDU 270 in which branch profiled portion 277 is in front and a non-split portion of elongated slot 273 follows. In this embodiment, the initial longitudinal portion of the elongated slot 273 in front of the branched portion has a converging profile such that the minimum width of the branched profiled portion 277 is formed at the maximum converging point of the initial portion. In essence, the nozzle is created by this unique profile, which can serve to accelerate the fiber before it enters the branched profile portion 277. The downstream unstiffened portion of the elongated slot 273 is defined by the parallel portions of the side walls 272, 274.

2D shows an embodiment of FDU 270 in which a branch-like profile portion 277 is formed by asymmetric branching sidewalls 272, In this embodiment, the side wall 274 is straight and essentially parallel to the longitudinal centerline of the elongated slot 273. The opposite side wall 272 is parallel to the side wall 274 at the top of the slot 273 and then branches to the outlet 275. In addition, the bifurcated profile of the diffusion chamber 280 is formed by the asymmetric branching side walls 282, 284. In alternate embodiments, the FDU 270 may have an asymmetric bifurcated profile and the diffusion chamber 280 may have a symmetrical bifurcated profile.

The embodiment of Figure 2D is similar to the embodiment of Figure 2E in that the sidewalls 274 of the FDU 270 and the sidewalls 284 of the diffusion chamber 280 are straight. In this particular configuration, the side walls 274 and 284 are disposed in the same plane and may constitute a continuous wall. The inlet 286 of the diffusion chamber 280 is still spaced from the outlet 275 of the FDU 270 by the space between the sidewalls 272 and 282.

2F, FDU 270 illustrates an embodiment of a small or "shorter" process line 200 that includes a shorter length dimension and similarly includes a branched profile portion 277 as compared to other embodiments . In fact, the longitudinal length of the elongated slot 273 may be less than the longitudinal length of the diffusion chamber 280. It should be understood that the benefits of the present invention can be realized in various sizes and configurations of the diffusion chamber and fiber elongation unit, including the symmetrical and asymmetric bifurcated walls of the fiber elongation unit and / or the diffusion unit.

Figure 2G shows an embodiment of FDU 270 in which an elongated slot 273 is formed by an initial converging section of walls 272 and 274 followed by a parallel section of walls 272 and 274. [ The parallel region is incorporated into the branched profile portion 277 formed by the asymmetric branch side walls 272, 274. In the illustrated embodiment, the converging / parallel / bifurcated profile of the elongated slot 273 is symmetrical about the longitudinal centerline of the slot 273. It is to be understood that any one or all of the other profile sections may also be asymmetric.

Generally, the fiber elongation unit may have an effective longitudinal length of the elongated slot of about 10 inches to about 100 inches. The length of one or all of the elongated slots may be diverged within the scope and spirit of the present invention. Thus, the magnitude of the branch will depend on the length and angle of the sidewalls and can be readily determined empirically by a person skilled in the art as a function of the process parameters. While not intending to limit the present invention, it is believed that in certain embodiments, the bifurcated profile portion should have an entrance width of from about 0.125 to about 0.60 inches, and the exit width of the bifurcated portion should be less than about 1.0 inch. In alternate embodiments, the total bifurcation angle (from one side wall to the opposite side wall) may vary within about 5 degrees or less.

3 (also see PCT Publication No. WO 2005/045116) illustrate an exemplary branched diffusion chamber 300 that is generally bounded by opposed sidewalls 310, 320. Electrostatic charging units 312 and 322 are located in the respective side walls 310 and 320, respectively. Electrostatic charging units 312 and 322 are arranged in a staggered pattern or in an offset configuration such that unit 322 is positioned closer to the elongated slot of fiber elongating unit 70 (Fig. 1) than electrostatic charging unit 312 . In alternate embodiments, charging units 312 and 322 may be positioned directly opposite each other. Further, when three or more electrostatic charging units are used, the staggered pattern of FIG. 2 may be continued, and the specific electrostatic charging units may be positioned directly opposite to each other and the other electrostatic charging units may be positioned in a staggered pattern. Lt; / RTI >

3, the sidewalls of the diffusion chamber include adjustment rods 314, 316 and 318 attached to the sidewalls 310 and adjustment rods 324, 326 and 328 attached to the sidewalls 320 ). ≪ / RTI > By manipulating the adjustment rods, the sidewalls 310, 320 can be moved relative to a particular vertical portion of the diffuser (the region of the diffuser, indicated by bracket A), before it begins to tilt or diverge outwardly from each other in the region of the diffuser, It is possible to constitute the diffusion chamber 300 so as to be substantially parallel to each other. It is also possible that the total length of the side walls 310, 320 is diverged from each other along the entire length. Other configurations may be possible and desirable depending on process variables such as fiber production speed, amount of drawn air to be guided through the diffusion chamber, and the like. For example, it may be desirable for the sidewalls 310, 320 to be very slightly convergent prior to branching forming a venturi nozzle or throat section.

Returning again to FIG. 1, a porous sheet of nonwoven fabric (not shown), such as a belt 110 disposed below the diffusion chamber 80 and fiber elongating unit 70, to receive the attenuated fibers 100 from the exit opening of the diffusion chamber 80 The forming surface is also shown. A vacuum source (not shown) disposed beneath the porous forming surface 110 can advantageously be employed to pull the attenuated fibers onto the porous forming surface 110. The fibers contained on the porous forming surface 110 include loose continuous fibers of a nonwoven web that can be initially merged, preferably using a merging means 130 to assist in transferring the web to the bonding apparatus. The merging means 130 may be a mechanical consolidation roll as is known in the art or may be a mechanical consolidation roll as disclosed in U.S. Patent No. 5,707,468 to Arnold et al. Or an air knife blowing air heated up or over the web.

The process line 10 further includes a coupling device, such as the calender rolls 150, 160 shown in Figure 1, which can be used to thermally point or bond the nonwoven web as described above. Alternatively, if the fibers are multi-component fibers with component polymers having different melting points, through-air bonders known to those skilled in the art can be advantageously utilized. Generally speaking, the air-entrainer combines a heated multi-component fiber web to produce a heated, low-melting polymer component having a temperature of at or above the polymer melting point of the low melting point polymer component and a temperature below the melting point of the high melting point polymer component Air is preferably used to form an inter-fiber bond. The web may be joined by using other means known in the art, such as adhesive bonding means, ultrasonic bonding means, or entanglement means such as hydroentangling or sealing.

Finally, the process line 10 further includes a winding roll 180 for winding up the combined web 170. Although not shown here, various additional possible processes known in the art, such as web slitting, stretching, processing, or lamination of nonwoven fabrics with other materials such as films or other nonwoven layers, and / Finishing steps may be performed within the spirit and scope of the present invention.

In another embodiment, the uniformity of the nonwoven web configuration can be further improved or improved using a vortex generator on or near the inner surface of the branched side wall of the diffusion chamber. The vortex generators may be disposed along one or more walls at spaced locations across the cross-machine direction of the sidewalls to induce vortex flow. The induced vortices will serve to increase the turbulence in the inner layer of air currents close to the sidewalls, which adds energy to the flow in the region, reduces flow separation, and more effectively cools the airflow to the sidewalls as the sidewalls diverge Thus providing a more complete machine direction dispersion of the airflow and consequently a larger machine direction fiber bundle spread. Vortices may be generated by having tabs or protrusions on one or more sidewalls at spaced locations as described in U.S. Patent No. 5,695,377 to Triebes et al., Which is incorporated herein by reference in its entirety . Depending on the arrangement of the vortex generators and the amount of machine direction fiber bundles deployed within the diffusion chamber, catching or dragging of the fibers to the vortex generator may be a problem. In such a case, it may be desirable to use an inverted tab or vortex generator dimple extending to the surface of the material forming the sidewall, rather than a vortex generator extending outwardly from the inner surface of the sidewall to the diffusion chamber.

Other methods of vortex generation may be employed with or in place of those described above. For example, one or more rearward facing stepped sections that proceed substantially in cross-machine directional width of the diffusion chamber may be used on the inner sidewall surface to create a vortex. As another example, air may be introduced into one or both of the sidewalls of the diffusion chamber at or near the branch point to create a vortex by blowing a fine jet of fluid, such as air through pores or holes drilled or otherwise formed in the sidewall surface material A jet can be used. As described generally in U. S. Patent No. 5,988, 522 to Glezer et al., The entire contents of which are hereby incorporated by reference, it is believed that, instead of actual air jets, It can be used for all. Generally described, the composite jet can be fabricated into a fluid-filled chamber having a rigid wall with a flexible actuating membrane at one end and a small hole at the other end. The flexible membrane can then be actuated repeatedly by acoustic wave energy, mechanical energy, or piezo energy to cause a jet of fluid (such as air) to be emitted from a hole in the wall that is more rigid at the other end of the chamber.

The following examples are provided for illustrative purposes only, and the present invention is not limited thereto.

Exemplary spunbond nonwoven materials are available from ExxonMobil Chemical Co. (Houston, Tex., USA) and have a melt flow rate of about 35, commonly referred to as Exxon 3155, Polypropylene was used. All materials were prepared using a spunbonded slot-elongated nonwoven spinning system as described in the above-mentioned U.S. Patent No. 3,802,817 to Matsuzaki et al., And all the materials after being collected on the forming surface were heated to a calender roll Lt; / RTI > As is generally described in the above cited PCT Publication No. WO 2005/045116, with respect to all materials, the electrostatic charging system was positioned near the draw slot exit of the fiber drawing unit to charge the filament curtain, Before entry, static charge is applied.

Further, in the manufacture of exemplary materials, as described in U.S. Patent No. 5,814,349 to Zeus et al., And generally as described above (except that the electrostatic charging unit is not located in the diffuser) Was positioned substantially below the fiber elongating unit elongation slot. The diffusion chamber was mounted slightly below the outlet of the fiber drawing unit to allow air to be drawn into the diffusion chamber. The diffusion chamber was set using a control rod to be manufactured in a venturi type and the sidewalls were initially converged before diverging at the bottom or outlet of the diffusion chamber.

The control sample (linear FDU) was fabricated using a fiber drawing unit (FDU) having parallel side walls with inlet openings and exit openings on FDUs of the same dimensions. An exemplary material (branched FDU) was fabricated using an FDU having a branched side wall with an exit opening larger than the inlet opening dimension. One set of exemplary materials was fabricated using an electrostatic charging system to impart charge onto the fibers. For all materials, the spinning and stretching conditions were kept constant. The polymer material throughput and fiber elongation were kept constant to produce the same fiber size. For all materials, the average diameter of the fibers was about 18 micrometers (about 2.0 denier).

The resulting nonwoven web was tested for air permeability using a TEXTEST FX 3300 air permeability tester, available from Schmid Corp. (Spanbergurg, SC) according to the ASTM D737 test method. The material was tested for air permeability and the results of 15 replicates for each sample were averaged for each material. Permeability results measured in CFM (3 square feet per minute) are shown in Table 1 below.

Table 1: Air permeability (CFM)

In this example, the air permeability is a measure of the airflow through the spunbond web. More numbers indicate lower pressure drop. Pressure drop is a direct indication of web configuration. The material of the better construction has a smaller pore structure that increases the pressure drop. Thus, a better configuration is represented by a lower permeability value. The data in Table 1 shows that the transmissivity value for the branched FDU sample is 11% to 13% lower than the comparative material. All of the materials in the table were of the same basis weight of about 0.50 osy (about 17 gsm) and were produced at the same polymer material throughput of about 10.6 PIH (about 190 kg / meter / hour). All other parameters are essentially constant, indicating that the branched FDU fabricates a better construction web.

Claims (47)

Providing a plurality of fibers from an extrusion apparatus; An inflation damping force that imparts a velocity to the fiber, the inflation damping force comprising a perturbed attenuating air supplied from at least one air nozzle configured in the FDU, into an elongated slot of an open system fiber drawing unit (FDU) having an inlet and an outlet Applying to the fiber; Transporting the fibers through the branched profiled portion of the FDU elongated slot to unfold the fibers in the machine direction within the FDU; Reducing the speed of the fibers in the branching diffusion chamber away from the outlet of the FDU; Applying a static charge applied in the diffusion chamber or FDU to the fiber; And Then collecting the web on the web on a transfer forming surface ≪ / RTI > The method of claim 1, The method of claim 1, wherein a static charge is applied to the fibers as the fibers are transferred through the FDU. 3. The method of claim 2, wherein a static charge is applied to an oppositely electrostatic charging unit in the FDU, wherein the one or more electrostatic charging units are located substantially closer to the diffusion chamber than the one or more other electrostatic charging units. The method of claim 1, wherein a static charge is applied to the fibers as they are transferred through the diffusion chamber. 5. The method of claim 4, wherein an electrostatic charge is applied to the oppositely electrostatic charging unit in the diffusion chamber. 2. The method of claim 1, wherein the attenuating air is supplied to the elongated slot in the FDU with one or more air nozzles configured on each opposing side wall of the FDU. 2. The method of claim 1, wherein the bifurcated profile portion of the FDU-elongated slot branches substantially continuously from a minimum width to a maximum width. 2. The method of claim 1, wherein the bifurcated profile portion of the FDU elongated slot is substantially continuously bifurcated between the elongated slot entrance and the exit. 2. The method of claim 1, wherein the bifurcated profile portion of the FDU-elongated slot is discontinuously branched from a minimum width to a maximum width. The method of claim 1, wherein the fibers are transported through the non-split portion of the elongated slot in the FDU upstream from the branched profiled portion of the elongated slot. An extrusion device for providing a plurality of fibers; An open system fiber drawing unit (FDU) arranged to receive a plurality of fibers from the extrusion apparatus, the FDU comprising an elongated slot in which fibers are attenuated, the elongated slot having an inlet and an outlet formed by spaced walls, ; At least a longitudinal portion of the elongated slot comprising a branched profile in the fiber transport direction through the FDU, the fibers being unrolled in the machine direction as the fibers are transported through the diverging profile portion of the FDU; A branching diffusion chamber spaced from the outlet of the FDU; At least one electrostatic charging unit configured to apply an electrostatic charge to the fibers in the diffusion chamber or the FDU; A transfer forming surface below said diffusion chamber from which fibers are collected; One or more air nozzles / RTI > Wherein the air supplied to the nozzle is perturbed and air exiting the nozzle enhances the machine direction diffusion of the plurality of fibers through air flow and agitation of the fibers. 12. The apparatus of claim 11, wherein the electrostatic charging unit is configured within the FDU to apply a static charge while fibers are being transported through the elongated slot. 13. The apparatus of claim 12, wherein the FDU includes an opposing electrostatic charging unit, wherein the one or more electrostatic charging units are positioned substantially closer to the diffusion chamber than the one or more other electrostatic charging units. 12. The apparatus of claim 11, wherein the electrostatic charging unit is configured in the diffusion chamber. 15. The apparatus of claim 14, comprising an opposing electrostatic charging unit within the diffusion chamber. 12. The apparatus of claim 11, wherein the bifurcated diffusion chamber is formed by opposed symmetrically branched sidewalls. 12. The apparatus of claim 11, wherein the branching diffusion chamber is formed by an asymmetric branching sidewall. 12. The apparatus of claim 11, wherein the bifurcated profile portion of the FDU elongation slot is formed by a symmetrically branched side wall. 12. The apparatus of claim 11, wherein the bifurcated profile portion of the FDU elongated slot is formed by an asymmetric branching sidewall. 12. The apparatus of claim 11, wherein the bifurcated profile portion of the FDU elongation slot branches substantially continuously between the elongated slot entrance and the elongated slot exit. 12. The apparatus of claim 11, wherein the bifurcated profile portion of the FDU elongation slot branches non-continuously. 12. The apparatus of claim 11, wherein the FDU elongation slot comprises an upstream non-branched portion adjacent the branch profiled portion. 23. The apparatus of claim 22, wherein the non-split portion is formed by substantially parallel sidewalls. 23. The apparatus of claim 22, wherein the non-split portion is formed by a converging sidewall. 12. The apparatus of claim 11, further comprising one or more air nozzles configured in the FDU to supply attenuating air to the bifurcated profile portion of the FDU elongation slot. 12. The apparatus of claim 11, wherein the bifurcated profile portion of the FDU elongated slot has an inlet width of 0.125 to 0.60 inches and an outlet width that is greater than the inlet width and less than 1.0 inch. 27. The apparatus of claim 26, wherein the FDU has a longitudinal length of 10.0 to 100.0 inches. 27. The apparatus of claim 26, wherein a longitudinal length of the FDU is less than a longitudinal length of the diffusion chamber. 12. The apparatus of claim 11, wherein the total divergence angle of the diverging profile portion of the FDU elongation slot is 5 degrees or less. Providing a plurality of fibers from an extrusion apparatus; Applying, to an elongated slot of an open system fiber drawing unit (FDU) having an inlet and an outlet, an air pressure damping force imparting a velocity to the fiber to the fiber; Transporting the fibers through the branched profiled portion of the FDU elongated slot to unfold the fibers in the machine direction within the FDU; And Collecting the fibers on the web on a transfer forming surface ≪ / RTI > The method of claim 1, 31. The method of claim 30, further comprising supplying at least one air nozzle with attenuation air to an elongated slot within the FDU. 31. The method of claim 30, further comprising supplying attenuation air to an elongated slot in the FDU with one or more air nozzles configured on each opposing sidewall of the FDU. 33. The method of claim 32, further comprising perturbing the attenuating air supplied to the air nozzle. An extrusion device for providing a plurality of fibers; An open system fiber drawing unit (FDU) arranged to receive a plurality of fibers from the extrusion apparatus, the FDU comprising an elongated slot in which fibers are attenuated, the elongated slot having an inlet and an outlet formed by spaced walls, ; At least a longitudinal portion of the elongated slot comprising a branched profile in the fiber transport direction through the FDU, the fibers being unrolled in the machine direction as the fibers are transported through the diverging profile portion of the FDU; A transfer forming surface on which the fibers are collected as a web; And At least one air nozzle configured in the FDU to supply attenuation air to the bifurcated profile portion of the FDU elongation slot, / RTI > Wherein the air supplied to the nozzle is perturbed and air exiting the nozzle enhances the machine direction diffusion of the plurality of fibers through air flow and agitation of the fibers. delete delete delete delete delete delete delete delete delete delete delete delete delete

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